1. Nawat Watanachai
Chiangmai University Hospital
2011

2. Computer
 What is computer

3. Computer
 ‘difference machine’
 1938

4. Guys who brought computer to us all
 1981

5. Guys who brought computer to us
all
ช่าย...
เราทำาสำาเร็จแล้
วอ่ะจ๊อบ
คอมพิวเตอร์ทก
ุ
ครัวเรือน
 today
และเราว่า
แมคกำาลังจะ
ขายดีกว่าวิน
โด้ฟร่ะบิลล์

6. Computers are everywhere

7. Why do ‘some’ computer users
develop CVS?
 Hardware : computer screen, room
 User : human eye
 computer tasks : The ways we use computer
ปวดตา
คร้าฟ
บร๊ะเจ้า...ช้าน
ปวดหัว...
ปวดตา
คร้า

8. 5 types of
vision-related components

9. 1. Computer screen
 Viewing a computer screen is much more visually
demanding than viewing a paper
 Computer screen
 self illuminated, not reflection
 Brightness : to bright/ unsteady
  visual fatique (Anshel, 2005)

10. 1. Computer screen
 High contrast, brightness  character blur
 Swithching between light and dark
background  fatique of the iris muscle
 Recommended
 Dark characters against light background display

11. 1. Computer screen
 Angle of viewing
 dry eyes and neck pain (Anshel 2005)
 Distance between eyes and screen
 Not easily adjusted,compared to books

12. 1. Computer screen
 Visual effects of display characteristics
 A. Display quality
 B. Lighting and glare
 C. Refresh rates
 D. Radiation

13. 1.Computer screen
A. Display quality
 ‘poor display quality probably contributes to
the annoyance and discomfort sometimes
reported by workers. Visual performance is
affected by a number of display parameters,
such as character size, structure, and style;
and by image contrast and stability’
 The US national research council committee on
vision, 1983.

14. 1. Computer screen
A. Display quality
 Resolution, Pixel-base dots
 Pixels : Dim on the outer edge
 Less resolution
 More blurred image
 hard to focus (Miyao 1989)
 High contrast  visual strain (Anshel 2005)

15. 1. Computer screen
A. display quality
 Pixels : Ziefle, Hum Factors 1998
 Viewing document, Compare 62 dpi VS 98 dpi
 Search reaction time and fixation durations were
increase significantly with 62 dpi

16. 1. Computer screen
B. lighting and glare
 surrounding sources of light
 Computer screen
 (overhead fluorescent, desk lamp, large windows)
 Reflection : image behind the computer
 Glare : wash out screen character images

17. 1. Computer screen
B. Lighting and Glare
 Glare increases the amount of time required to read
relatively easy passages. (Garcia, Hum Factors 1985)
 Surrounding luminance  reduce the accommodation
amplitude. (Wolska, Int J Occup Saf 1999)
  annoyance and visual fatique
 NOT chronic visual disorder

18. 1. Computer
screen
C. refresh rates
 Refresh rate (Hz)
 Critical fusion frequency = 30-50 Hz
 Extremely low rate of ‘flicker’ (8-14Hz) can
induce epileptic seizure
 Percieved flickers  annoyance, fatique,
headache
 Recommended frequency = at least 75 Hz 
synchronous ERG response

19. 1. Computer screen
C. Refresh rate
 Refresh screen
 (Blehm 2005, Jaschinski 1996, Kennedy 1991)
 Need >75Hz
 Should be >300Hz
 LCD VS CRT

20. 1. Computer screen
D. radiation
 Ionizing radiation
  cellular change
  tissue damage
 VDT
 NOT emit alpha, beta, gamma, x ray
 NO study shows any hazard

21. iPad
 9.7-inch (diagonal) LED-backlit glossy
widescreen Multi-Touch display with IPS
technology
 132 dots per inch (dpi)
 Refresh rate at 200 Hz

22. iphone
 Retina display
 3.5-inch (diagonal) widescreen Multi-Touch




display
960-by-640-pixel resolution at 326 dpi
Refresh rate at 200 Hz
800:1 contrast ratio (typical)
500 cd/m2 max brightness (typical)

23. Samsung Galaxy Tab10.1
 WSVGA(1,024 x 600)
 7.0"
 124 dpi
 Refresh rate 180 Hz

24. 2. Computer room
 ‘lighting condition’ is the most important part
 Ideal computer environment
 40-50Fc of ambient light
 Non-computerized office 100 Fc
 sun in an average outdoor setting 8,000-12,000 Fc
 Indoor direct light at noon :1500 Fc
 To bright  visual discomfort

25. 2. Computer room
 Equilized brightness
 Source of light (overhead flu, windows, desk
lamps)
 To close
  reflection and glare  back and forth focusing
  reduce visibility of the screen
  discomfort
 Other factors : bright-white clothing, light-
color desk surface, highly polished furnitures,
large mirrors

26. 2. Computer room
 Types of lighting
 Natural light
 Filament lamps (+)
 Luminescent lamps (-)
 Sodium lamp (+++)
 most conductive to visual capacity
 (Blehm 2005)
 Mercury-arc lamps (+)

27. 2. Computer room
 Non-light factors (Sheedy 1997)
 Air flow (-)
 Temperature (-)
 Humidity (+)

28. 3. Human eyes
 Eyes are relaxed and comfortable viewing
object at a long distance (>6m)
 but need a lot more muscles viewing near
object (<30cm).
 we need tears covering our eye surface
 Preserve moisture and O2 supply
 Keep the eye surface smooth and comfortable

29. 3. Human eyes
 Blinking : clean off and refresh tearfilm
 Blink rate (Freudenthaler 2003, Kadner 2004)
 Normal : 15-16 blinks/min
 Computer use : 5-6 blinks/min
 Viewing angle
 Lower in reading books : less exposure
 Higher in computer works : more exposure

30. 3. Human eyes
 Eyes need to adjust in order to see objects from
different distances
 Computer screen < paper on the table
 Focus–refocus–refocus-refocus…. -L-’
 Headache and blurred vision

31. 4. Computer users
 Computer users wearing corrective lens
early and more severe CVS
 CL wearers
 Youngers  myopia?
 253 kids, 6-10YO (Hoenig 2002)
 Elders (surface abn, tear abn)

32. 5. Computer tasks
 Tasks : studying, browsing, shopping,
communication, business
 Eg.
 Data entry workers : paper > screen
 Graphic artists : screen > paper
 Gamers : screen
 It will be more CVS with
 More time on the screen
 Reading small fonts on the screen
 Action games